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  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      class Animal {
        // toString(){}
        // Animal.prototype.__proto__===Object.prototype
      }
      class Cat extends Animal {
        // toString() {}
        // Cat.prototype.__proto__
      }
      class TomCat extends Cat {
        constructor() {
          // return this;
        }
        // toString(){}
        // TomCat.prototype.__proto__
      }
      const tc = new TomCat();

      console.log(tc.toString);
    </script>
  </body>
</html>
